The subject matter disclosed herein relates to a communication system and, in particular, to an enhanced frequency modulation (FM) technique for use in a communication system.
Frequency modulation and forms of frequency modulation, such as continuous-phase frequency-shift keying (CPFSK) and Gaussian minimum shift keying (GMSK), are widely used in data transmission systems for a variety of reasons. For instance, FM data transmission systems are easy to demodulate (e.g., do not need automatic gain control (AGC), Costas loop, or IQ mixers) and are capable of fast acquisition (i.e., no need to recover phase). Further, FM data transmission systems are robust (i.e., insensitive to linearity and impulse noise), can be employed with single chip receiver solutions, provide efficient class C power amplification (i.e., emit less heat and has longer battery life), and can be implemented at low costs.
Although FM data transmission systems provide these advantages, the FM signals produced by the FM data transmission systems are generally less spectrally efficient than signals generated by linear modulation systems, such as quadrature amplitude modulation (QAM). Generally, the spectral efficiency of FM data transmission systems may be improved by filtering a baseband modulating signal, but the improved spectral efficiency is limited due to spectral components in the FM signals that extend beyond the baseband bandwidth on each side of the FM signals. While these spectral components can be reduced by lowering the FM deviation, the reduced FM deviation also lowers the signal to noise ratio in the FM signals.